1. Field of the Invention
Embodiments of the invention relate to the field of device manufacturing. More particularly, the present invention relates to a method, system and structure for patterning a substrate and for implanting into a substrate for manufacturing a device.
2. Discussion of Related Art
Optical lithography is often used in manufacturing electronic devices. It is a process by which a substrate is patterned so that circuit may be formed on the substrate according to the pattern. Referring to FIG. 1a-1e, there are shown simplified illustrations of the optical lithographic process. Generally, the substrate 112 is coated with photo-curable, polymeric photoresist 114 (FIG. 1a). Thereafter, a mask 142 having a desired aperture pattern is disposed between the substrate 112 and a light source (not shown). The light 10 from the light source is illuminated onto the substrate 112 via the aperture of the mask 142, and the light transmitted through the mask's aperture (or the image of the pattern) is projected onto the photoresist 114. A portion of the photoresist is exposed to the light 10 and cured, forming cured photoresist portion 114a, whereas the rest of the photoresist remains uncured, as illustrated by uncured photoresist 114b (FIG. 1b). As a result, an image of the mask's aperture may be formed by the cured photoresist portion 114a. 
As illustrated in FIG. 1c, the uncured photoresist 114b is stripped, and 3D photoresist feature or relief 114c corresponding to the mask's aperture pattern may remain on the substrate 112. Thereafter, the substrate is etched, and trenches 116 corresponding to the negative image of the mask's aperture pattern may form (FIG. 1d). After the uncured photoresist 114b is removed, a patterned substrate 112 may form (FIG. 1e). If a metallic layer is deposited on the trenches, a circuit having a desired pattern may be formed on the substrate 112.
Referring to FIG. 2, there is shown a conventional optical lithographic system 200 for projecting the image of the mask's aperture pattern to the substrate. The optical lithography system 200 comprises a light source 222, an optical integrator 232, and a condenser lens 234. In addition, the optical lithography system 200 comprises mask 142 having a desired aperture pattern and a projection lens 252. As illustrated in the figure, light having desired wavelength is emitted from the light source 222 to the optical integrator 232 and the condenser lens 234, which are collectively known as an illuminator 230. In the illuminator 230, the light 10 is expanded, homogenized, condensed, or otherwise conditioned. The light 10 is then illuminated onto the mask 142 having the desired aperture pattern to be projected onto the substrate 112. The light 10 transmitted through the apertures of the mask 142 may contain the information on the mask's aperture pattern. The light 10 is then captured by the projection lens 252 which projects the light 10 or the image of the mask's aperture pattern onto the photoresist deposited on the substrate 112. In projecting the image, the projection lens 10 may reduce the image by a factor of four or five.
To generate circuit patterns with smaller feature size (e.g. width of the trench), several modifications have been implemented into the process. As known in the art, the ability to project a clear image of a small feature may depend on, among others, the wavelength of the light used in the process. Currently, ultraviolet (UV) light with wavelengths of 365 nm and 248 nm, and 193 nm are used.
Although optical lithography is an efficient process with high throughput, the process is not without disadvantages. One limitation is the inability to print accurate openings or holes within a resist material as the opening size scales smaller. As the opening dimension scales to smaller dimensions, the lithography system loses imaging resolution. Additionally, during the development and removal stages, less material may be removed in lower portions of a three dimensional opening in resist, as illustrated in FIGS. 1f-1h. As depicted in FIGS. 1f-1g, the resist layer 160 includes multiple circular openings 164 which are tapered such that the dimension is smaller at the substrate interface. After substrate etching, this may lead to smaller than desired vias 166 in the underlying substrate 162, as shown in FIG. 1h. In addition, resist residue may remain at the interface between the circular opening 164 and substrate 162, preventing proper etching of the underlying substrate 162 in subsequent processing steps so that non-uniform substrate vias 166 form.
A further problem is illustrated in FIG. 1i, in which openings 172 are formed in resist 170. FIG. 1i depicts rough and irregularly shaped openings 172, which are typical of very small resist openings. As opening dimension shrinks, particularly below about 100 nm, roughness associated with the opening may be a significant fraction of the total nominal size of the opening, as depicted. The roughness of small features is known as line width roughness (LWR) or line edge roughness (LER) in the context of printed resist features, such as lines, and is used hereinafter also to refer to roughness characteristics in resist openings. As known in the art, LWR is excessive variations in the width of the photoresist feature formed after uncured photoresist 114b is stripped from the substrate. If the variations occur on the side surface of the photoresist relief or feature, the variations is known as LER. Because the geometrical shape of a patterned resist feature such as a rough opening is transferred from a resist layer to an underlying permanent layer of a device during patterning of the underlying layer, LWR and LER can limit the ability to form trenches or vias of acceptable quality for small opening dimensions, such as those below about 100 nm in lateral size. Such variations may lead to non-uniform circuits and ultimately device degradation or failure.
Several approaches have been proposed to address the printing of small openings in resist. One technique involves printing relatively larger openings in a resist material, followed by introducing chemicals into the resist to swell the resist and thereby shrink the size of the opening. Other known techniques, including shrink assist film for enhanced resolution (SAFIER™), and cross contact double patterning, are complex and involve multiple steps to implement.
In view of the above, it will be appreciated that there is a need to improve resist lithography processes for technologies requiring very small opening sizes, such as for sub-100 nm CD devices.